1. Technical Field
The present invention generally relates to biomedical devices such as ophthalmic lenses.
2. Description of Related Art
Biomedical devices such as contact lenses are made of various polymeric materials, including rigid gas permeable materials, soft elastomeric materials, and soft hydrogel materials. The majority of contact lenses sold today are made of soft hydrogel materials. Hydrogels are a cross-linked polymeric system that absorb and retain water, typically 10 to 80 percent by weight, and especially 20 to 70 percent water. Hydrogel lenses are commonly prepared by polymerizing a lens-forming monomer mixture including at least one hydrophilic monomer, such as 2-hydroxyethyl methacrylate, N,N-dimethylacrylamide, N-vinyl-2-pyrrolidone, glycerol methacrylate, and methacrylic acid. In the case of silicone hydrogel lenses, a silicone-containing monomer is copolymerized with the hydrophilic monomers. Regardless of their water content, both hydrogel and non-hydrogel siloxy and/or fluorinated contact lenses tend to have relatively hydrophobic, non-wettable surfaces.
In the field of biomedical devices such as contact lenses, various physical and chemical properties such as, for example, oxygen permeability, wettability, material strength and stability are but a few of the factors that must be carefully balanced in order to provide a useable contact lens. For example, since the cornea receives its oxygen supply from contact with the atmosphere, good oxygen permeability is an important characteristic for certain contact lens material. Wettability also is important in that, if the lens is not sufficiently wettable, it does not remain lubricated and therefore cannot be worn comfortably in the eye. Accordingly, the optimum contact lens would have at least both excellent oxygen permeability and excellent tear fluid wettability.
It is known that increasing the hydrophilicity of a contact lens surface improves the wettability of the contact lenses. This; in turn, is associated with improved wear comfort of the lens. Additionally, the surface of the lens can affect the overall susceptibility of the lens to deposition of proteins and lipids from the tear fluid during lens wear. Accumulated deposits can cause eye discomfort or even inflammation. In the case of extended wear lenses, i.e., a lens used without daily removal before sleep, the surface is especially important, since extended wear lenses must be designed for high standards of comfort and biocompatibility over an extended period of time. Accordingly, new formulations that have the potential to yield improved surface qualities are still desirable.
Karunakaran et al., “Synthesis, Characterization, and Crosslinking of Methacrylate-Telechelic PDMAAm-b-PDMS-b-PDMAAm Copolymers”, Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 45, pp. 4284-4290 (2007) (“Karunakaran et al.”) discloses the preparation of a new amphiphilic methacrylate-telechelic pentablock copolymer by reversible addition fragmentation chain transfer (“RAFT”) polymerization. Karunakaran et al. further discloses that the new amphiphilic methacrylate-telechelic pentablock copolymers can be used in an ophthalmic application such as in the formation of a contact lens. However, the process for making the amphiphilic methacrylate-telechelic pentablock copolymers is time consuming and employs different reagents and process conditions. This, in turn, can cause reproducibility problems. In addition, the methacrylate-telechelic copolymers prepared by Karanakaran et al. are cross-linking agents, which can increase the “effective” cross-link density of the resulting product resulting in a higher modulus of the product.
It would therefore be desirable to provide improved biomedical devices such as contact lenses that exhibit suitable physical and chemical properties, e.g., oxygen permeability, lubriciousness and wettability, for prolonged contact with the body while also being biocompatible. It would also be desirable to provide improved biomedical devices that are easy to manufacture in a simple, cost effective manner.